Control circuit for controlling the rollers of calenders



April 8, 1969 ULL ET AL 3,436,913

CONTROL CIRCUIT FOR CONTROLLING THE ROLLERS OF CALENDERS Filed Dec. 27, 1966 Sheet CONTROL CIRCUIT FOR CONTROLLING THE ROLLERS OF CALENDERS Sheet Filed Dec. 27. 1966 Figjg States Filed Dec. 27, 1966, Ser. No. 604,788 Claims priority, application Germany, Jan. 3, 1966,

K a 3 Int. Cl. F15]: 11/16, 13/06, 13/09 US. Cl. 6051 7 Claims ABSTRACT OF THE DISCLOSURE A hydraulic system for use in connection with the rollers of a calender, which includes pressure pumps or fluid pressure accumulator means, and in which for purposes of placing the rollers under pressure, both surfaces of differential pistons operatively connected to said rollers are actuated by fluid under pump pressure, whereas for venting purposes, the smaller surfaces only of said differential pistons receive fluid under pressure from both said pumps and said accumulator means until the accumulator pressure has dropped to that of the pump pressure, whereupon the connection of the accumulator means with the pressure line of the pumps is blocked, and the pumps deliver pressure fluid to said smaller differential piston surfaces only.

The present invention relates to a fluid pressure operable device for venting calender rollers and subjecting the same to pressure, especially calender rollers in supercalenders for satining paper, in which by hydraulic cylinders arranged at the top a downward pressure is exerted upon a set of rollers by exerting a pressure on the top of a presure piston, whereas when exerting a pressure upon the bottom of the piston, the set of rollers is Vented or relieved or pressure.

Inasmuch as with raw papers coming from the paper machine it is possible in view of the screen portion that the paper will have a different thickness at opposite marginal portions, it has become known to provide each calender side with a pressure pump of its own having control members of its own so that different pressures can be adjusted for each calender side. In customary manner each pressure pump has furthermore associated therewith a hydraulic pressure accumulator in order to obtain the required buffer effect and to create a pressure reserve. Devices of this type have the drawback that the venting or pressure relieving operation cannot be carried out fast enough. On the other hand, the speed at which the venting is effected is of foremost importance for the life of the rollers because when paper tears occur, folds can form in the paper which damage the elastic as well as the chilled iron rollers so that in such an instance it is imperative that the rollers of the roller set can be moved away from each other as fast as possible.

The above mentioned design has the further drawback that when exerting pressure upon the top of the hydraulic piston of the pressure cylinder, the pressure exerted upon the paper web will be too high because to this pressure there has to be added the considerable weight of the rollers when multi-roller supercalenders are employed. Since the exertion of pressure is effected at the high pressure required for the venting of the rollers, it is desirable to reduce the hydraulic pressure when the rollers are pressed together. While this could be effected by fast working pressure reducing valves, such valves are for pressures up to 200 atmospheres above atmospheric pressure so expensive that the employment thereof is no longer economically feasible.

3,436,913 Patented Apr. 8, 1969 It is, therefore, an object of the present invention to provide a fluid pressure operable device for calenders, which will overcome the above mentioned drawbacks.

It is another object of this invention to provide a device as set forth in the preceding paragraph which will be able in a simple manner to reduce the pressing force in the working position roller pressure.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatic illustration of a conduit and electric control system according to the invention.

FIG. 1a diagrammatically illustrates the rollers of a calender and their connection with cylinder piston means shown in FIG. 1.

FIG. 2 is a diagram showing the course of the pressure and movements in the pump, in the pressure accumulator and in the pressure piston in conformity with the time.

The fluid pressure operable device according to the invention is characterized primarily in that the control valves for controlling the placing of the rollers under pressure and for venting the rollers are electrically controlled or mechanically coupled in such a way that when exerting pressure, the pressure cylinders of both piston sides are subjected to pressure, whereas in the working position venting the control valve for the venting operation alone will convey pressure to the bottom surface of the piston. In this way, when conveying pressure, only the differential pressure between the two piston surfaces the piston top and bottom surfaceswill be effective, and it is thus possible by correspondingly dimensioning the cross section of the piston rod to reduce the pressing force of the pressure cylinder by up to 50% of the pressure force corresponding to the cross section of the pressure cylinder.

According to a further development of the invention, the connecting conduit between the pressure accumulator and the pressure conduit of the pressure pumps has interposed therein a check valve in such a blocking direction that when the pump pressure is the greater pressure, the pressure accumulator can not be filled. This in turn brings about that with a lifting operation of the rollers which requires a very high pressure, the total pressure of the pressure accumulator will be available at the start of the venting operation which pressure, however, will rapidly drop. During this time period, however, the pressure pumps have already reached their full speed so that now the pressure of the pressure pumps will be the greater pressure, and the pressure pumps will alone carry out the completion of the venting operation inasmuch as the pressure accumulators are during this operation not filled. With heretofore known installations, however, it was necessary that the pump which had reached its full speed, in addition to the venting operation, also had to fill the pressure accumulator whereby the entire venting operation was retarded.

Referring now to the drawing in detail, the two calender sides have respectively associated therewith separate hydraulic pumps 1 and 2 (see FIG. 1) which are adapted to press the pressure medium from a storage vessel 3 into pressure conduits 4 for the left side and into pressure conduits 5 for the right side of the calender. Both calender sides have in common a hydraulic pressure control valve 6 and a hydraulic venting valve 7, both valves being connected to both the conduit 4 and the conduit 5. The drawing shows the two control valves, operable for instance electrically, in non-energized condition. This condition corresponds to the working position roller load. The conduits 11 and 12 leading to the upper piston chambers, and the conduits 14 and 15 leading to the lower piston chambers (see FIG. 1a) are connected to the return conduit 13 so that in the pressure cylinders 9 and 10 no pressure prevails and, consequently, the rollers engage each other only due to their own weight. This condition roller load can also at any time of operation be produced by opening the normaHy closed switch 27.

When the normally open switch 28 is closed, the energizing circuit including conductors 2-6, 26", and 28' for both control values 6 and 7 is closed as a result of which both control spools 6a, 7a move to their right-hand position whereby hydraulic pressure is conveyed into the cylinder chambers above and below the pistons 16. As a result thereof, the device is placed into working condition roller pressure. The circuit according to the present invention brings about that in a simple manner in view of the differential effect of both piston surfaces, the rollers are subjected to considerably less pressure than would be the case if the upper pressure chamber only would receive fluid pressure. It is, of course, also possible in conformity with the invention that in heretofore customary manner when exerting pressure, only the upper cylinder chambers will receive pressure fluid. In such an instance, the conductor 26" is to be disconnected from conductor 26, in other words is to be omitted.

Finally, there will be described a further working position, namely the operation roller venting which is improved according to the present invention. The fast almost instantaneous venting of the roller set is necessary when, for instance, the paper web passing between the roller tears. During such an incident, folds can form in the paper web which damage not only the elastic rollers but also the cast iron rollers. The working operation roller venting is initiated by closing the normally open switch 26 and opening switch 28. The closure of said switch may also be initiated by a control device, for instance a photoelectric control device, which scans the paper web. In such an instance, the venting control valve 7 only is actuated, and the pressure pumps are turned on whereby through conduits 14 and 15 pressure is conveyed to the bottom side of the pistons 16 thereby lifting the roller set 33 by lifting spindles 34 and abutments 35. At .the same time, the pressure medium passes from the pressure accumulators 19 through check valves 21 into the pressure conduits 4 and 5. Since, however, the pressure in the pressure accumulators drops rather rapidly, it was necessary, with heretofore known devices of the type involved, that the pressure pump which in the meantime had reached its full speed not only convey the pressure medium into the pressure cylinders but also at the same time fill the pressure accumulators. In order to be able to take advantage of the full delivery possibility of the pressure pump for a quick lifting of the pressure .piston, the present invention provides that in the connecting conduit 20 between the pressure accumulators and the main pressure conduits 4 and there is interposed a check valve 21 in such a blocking position that when the pressure in the accumulator drops below the working pressure of the pumps, the delivery of the pressure medium to the pressure accumulator will be interrupted, and the pumps will deliver pressure fluid into the pressure chamber below the pistons 16.

According to a further development of the invention, the pressure accumulators are through the intervention of shunt conduits 22 in communication with the pressure conduits 11 and 12, said shunt conduits 22 likewise having a check valve 23 interposed therein. These shunt conduits have the purpose to permit the refilling of the accumulators when pressure is conveyed to above the pressure piston 16. Moreover, the check valves 23 prevent an emptying of the accumulators through the shunt conduits 22 at the operation roller load. Therefore, the accumulators are filled during the working position roller load which follows the venting operation, or are filled during roller load when circuits are employed without valves 24.

This refilling operation can also be controlled by control valves which are indicated in the drawing in dash line position. In such an instance, the control valves 24 are located in connecting conduits 25 leading to the main pressure conduit. These conduits are open only during the working position roller load or pressing whereas in the working position roller venting the said conduits are closed in view of the shunt arrangement with the venting valves 7.

The device according to the present invention brings about that the time required for the venting operation will be reduced by more than 50%. This will best be understood in connection with the venting-time diagram of FIG. 2. The dash line curve 29 represents the pump characteristic. The starting time Ta of the pump is characterized by the flat portion of the curve. The heavy curve 30 up to point 31 shows the quantity of pressure fluid delivered by the accumulators during the first phase of the venting operation. With heretofore known devices of the type involved, approximately at point 31 pressure equalization occurred between the decreasing accumulator pressure and the increasing venting pressure caused by the lifting of the rollers, and the time-stroke curve of the piston movements followed the thin line 32 because the pump in addition to feeding pressure fluid into the pressure cylinders also had to deliver pressure fluid into the accumulators for filling the same. In contrast thereto, due to the fact that the pressure accumulators are, following the reduction of the pressure up to point 31, disconnected from the pump, the full delivery of the pressure pump is conveyed to the pressure cylinders so that the time-stroke curve of the pressure pistons will follow the line 29. The gain in time between the heretofore known device and the device according to the invention thus amounts to Tg seconds which is more than half the time heretofore required for the full venting stroke.

It is, of course to be understood that the present invention is, by no means, limited to the particular construction shown in the drawing but also comprises any modifications within the scope of the appended claims. Thus, the present invention is also applicable to hydraulic devices in which both calender sides are provided with a common pressure pump with pressure accumulator.

What we claim is:

1. A hydraulic system for use in connection with the rollers of a calender to selectively press said rollers to ward each other and moving said rollers away from each other, which includes: double acting fluid pressure operable diiferential surface piston means, pump means operable to supply pressure fluid to the differential surfaces of said piston means for selectively moving said piston means in a first direction to press the calender rollers toward each other and to move said piston means in a second direction to move the calender rollers away from each other, fluid pressure accumulator means operable to de liver pressure fluid to said piston means to supplement the pressure fluid delivered by said pump means for moving said piston means in said second direction, valve means interposed between said pump means and said piston means to control the flow of fluid therebetween, and fluid pressure responsive means operable in response to the fluid pressure developed by said pump means at least equalling the pressure of the pressure fluid delivered by said accumulator means to said piston means to interrupt fluid communication between said piston means and said accumulator means and between the latter and said pump means.

2. A hydraulic system according to claim 1, in which said valve means is operable to convey pressure fluid from said pump means simultaneously to opposite sides of said piston means for moving the latter in said first direction.

3. A hydraulic system according to claim 1, in which said valve means includes a first valve movable to a first position for establishing communication of the larger surface side of said differential surface piston means with the pressure side of said pump means and also movable to a second position for establishing communication of said larger surface side with a fluid storage tank, said valve means also including a second valve movable to a first position for establishing communication of the smaller surface side of said difierential surface piston means with the pressure side of said pump means and also movable to a second position for establishing communication of said smaller surface side with a fluid storage tank.

4. A hydraulic system according to claim 1, in which said fluid pressure responsive means is formed by check valve means.

5. A hydraulic system according to claim 1, which includes check valve means interposed between said piston means and said accumulator means and operable in response to pressure fluid being supplied to the larger surface side of said differential surface piston means to establish communication between the pressure side of said pump means and the interior of said accumulator means for charging the latter.

6. A hydraulic system according to claim 1, in which said valve means comprises a first valve controlling the flow of fluid t0 and from the smaller surface side only of said piston means, and also comprises a second valve controlling the flow of fluid to and from the larger surface side only of said piston means.

7. A hydraulic system according to claim 6, in which said two valves are electrically solenoid controlled and in which thhe electric control circuit for the respective solenoid of said valves includes a first switch operable to simultaneously control said solenoids of said first and second valves and also includes a second switch operable to control only that solenoid which pertains to said first valve.

References Cited EDGAR W. GEOGHEGAN, Primary Examiner.

US. Cl. X.R. lO0-170 

